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The schedule file is a simple
ASCII file which contains information
about targets and calibrators to be observed by the KI. There is one
line of information per target or calibrator, plus comment lines.
The format of the lines in the schedule file is described below, and has been adopted as the standard for exchanging this information between KI observers, the MSC and the Keck Observatory (WMKO). Using this adopted format, KI observers send their MSC contact scientist their list of targets and calibrators, which after being reviewed and checked at the MSC, is incorporated into a nightly schedule file containing all observations to be made on a given night, and sent to WMKO for execution. Please send your schedule file to your MSC contact scientist in a simple email. In this email, you may also communicate your wishes about how the observation should be conducted (e.g. order in which to observe a given set of target and calibrators, how many observations -- a.k.a. scans -- are desired, etc). These suggestions may also be indicated in the comment lines of the schedule file itself, as indicated below. It is crucial that all the information in your schedule file be accurate, if you have any questions about any of the fields, please contact your assigned contact scientist or visit the the help desk page. Although a schedule file can be prepared by simply manually collecting all the required fields into the required format, we strongly recommend the use of the MSC getCal software, as it automatically searches the Hipparcos catalog for suitable calibrators given user-selectable sets of constraints, and generates its output in the schedule file format. Format of Schedule FilesThe following is an example of a section of a schedule file, which might contain information about KI observing of one of your targets:
The first 3 lines are comments. Comment lines begin with the character #. You may insert as many comment lines as you wish. Then follow 7 lines which specify a sequence of alternating observations of calibrators (lines with the tag "cal" near the end) and the target object (lines with the tag "trg" at the end). The order of the sequence is relevant: it indicates, in this case, that you wish to begin with a calibrator observation (always a good idea) and the order in which you want the different calibrator candidates to be observed. In some cases, the science program requires that a whole block such as the above one be repeated multiple times, and you may indicate so in your comment lines. Format of target linesColumns 1-12 are required. The line must end with with the tag "trg".Column 1: Target name (limit 15 characters) Format of calibrator linesColumns 1-12 are the same and
are required. Columns 13 to the end are
optional, but MUST end with the tag ``cal target'', where target is
the exact name of the target from its schedule file line.
As shown in the example above, it is customary to use the comment fields as follows: Column 13: spectral type Rules on source namesSource names must have no
spaces, punctuations or control
characters. For sources with more than one name, please be consistent
in your use of names throughout your schedule file. Maintaining this
consistency among different runs will also help you identify your
sources when you retrieve your data.
Tips on Choosing CalibratorsThe fringe visibility measured
on a target must be calibrated for
instrumental and atmospheric terms using observations of stars of
known visibility. Calibrator stars must therefore be either unresolved
by the KI (visibility = 1.0) or of known angular size. Because the
instrumental and atmospheric conditions change during the night, it is
necessary to measure calibrators frequently, typically interleaved
with the target observations. Since it is in general difficult to
estimate accurate angular sizes for stars, it is best to use
unresolved stars as calibrators whenever possible.
How do I know when a star is unresolved by KI? A star is unresolved to KI if it gives a visibility which is indistinguishable from 1.0, given the errors in the measurement. In general, the visibility that one would measure on a star of a certain diameter depends on the star geometry, declination, hour angle, and wavelength of observation. However, we can estimate a maximum calibrator size as follows, this estimate can be safely used to guide the selection of unresolved calibrators: Assume a 5% measurement error, a maximum projected baseline given by the KI physical baseline length (about 85 meters), and K-band observations; one can easily calculate that a star of uniform disk angular diameter of about 1 mas or smaller would appear unresolved. Other criteria must be carefully considered when selecting calibrators for your observing program. In summary, calibrators must be:
How many calibrators do I need? In principle, a single good calibrator is sufficient. However, because at the resolution of the KI many stars are unknown binaries, one should provide a minimum of 3 calibrators per target (although calibrators can be shared among nearby targets). If one of the calibrators has already been observed at KI and is known to be unresolved, a minimum of 2 calibrators should be provided. Using getCal to Choose Calibrators and Compose Schedule FilesThe criteria described above
for selecting calibrators are all
possible input constraints to the getCal program (and its graphical
interface gcGui). Moreover, getCal estimates calibrator angular
diameters, both from simple stellar model tables and from fits to
spectrophotometry data; and warns for multiplicity and variability
based on the Hipparcos catalog. Finally, getCal can easily retrieve
and use 2MASS photometry, and outputs its results in the format used
in schedule files. For all those reasons, getCal is the prefered
method for searching calibrators and composing schedule files. Please
refer to the getCal manual
for a complete description of its many features and some illustrative
examples.
If you are using getCal installed on your own machine, you may want to set the getCal defaults appropriately, see getCal environment variables for details. Provide Additional Information on your TargetsWe strongly encourage that you
provide your MSC contact scientist with
finding charts for those sources for which there is potential for
source confusion (faint object in crowded filed). The prefered
field-of-view for these charts is that of the Keck telescopes
acquisition camera: 2x2 arcmins.
In addition, please also include any relevant finding notes for a given target in your schedule file, as comment fields. If you are aware of any other peculiarities about your targets, please also include the appropriate comments in your schedule file. Examples of properties that may impact the efficiency of your KI observations are: source confusion (as described above), spatial extension on scales larger than about 0.05 arcsecs in the visible or near-infrared (will impact the performance of the adaptive optics and angle tracker sub-systems), and variabily (if you know that your target is variable, please include a comment on what you know about the likely minimum and maximum magnitudes in the appropriate band, visible and/or near-infrared). As a KI principal investigator, you share with your MSC contact scientist responsibility for planning your observation ahead of time as well as possible, in order to make efficient use of your awarded time. Please follow the guidelines above in order to insure good communication with your contact scientist about the details of your observing program. If instead of being expected and planned for, special difficulties arise during observing, it is likely that efficiency and therefore the time spent on your targets will be significantly reduced. |